Monopole antennas are a common and inexpensive way to radiate an omnidirectional signal. The vertical radiator of a basic monopole antenna may include a ground to plane redirect a portion of the radiated electromagnetic energy over the surface of the earth. Otherwise a portion of the radiated energy may be lost, constructively cancelled, or dissipated. The ground plane may comprise the earth's surface or an artificial metallic or conductive plate that serves as an electromagnetic field reflector. The present disclosure, however, concerns an improvement to artificial ground planes. A monopole antenna having an artificial conductive plate ground plane, for example, simulates the function of a dipole antenna. Furthermore, the functionality of a monopole antenna with a sufficiently large ground plane approaches that of a dipole antenna.
Standard monopole antennas are vertically polarized elements that may produce an electromagnetic field over a ground plane. Monopole antennas produce null emissions at their zeniths, which make them ill suited for short range communications at high incident angles. The null at zenith also prevents full hemispherical coverage which is more important in airborne links from a ground station.
Previous techniques to fill null emission patterns included bending the monopole element. Unfortunately, this technique requires extraordinary precision and advanced manufacturing methods, especially at high frequencies. Bending of the monopole element also distorts the azimuthal symmetry of the pattern.
It is therefore an object of the present invention to provide a new antenna with a structure to partially obviate null emission patterns at its zenith.
It is further an object of the present invention to provide an existing antenna with a ground plane structure to at least partially fill otherwise null emission patterns at its zenith.
It is another object of the present invention to provide an antenna with an inexpensive mechanism to reduce null emission patterns at its zenith without bending the radiator element.